Question

Which situation is work not being done? A) A bookcase is slid across carpeting. B) A stack of books is carried at waist level across a room. C) A chair is lifted vertically with respect to the floor. D) A table is dropped onto the ground. '

Answer 1

Answer:

B) A stack of books is carried at waist level across a room

Explanation:

Work is defined as:

$W=Fd cos \theta$

where

F is the force applied

d is the displacement of the object

$\theta$ is the angle between the direction of the force and of the displacement

From the formula, we see that the work done is zero when the force and the displacement are perpendicular to each other. Let's now analyze each situation:

A) A bookcase is slid across carpeting. --> work is done, because the force that pushes the bookcase is in the same direction of the displacement

B) A stack of books is carried at waist level across a room. --> no work is done, because the force to carry the book is vertical, while the displacement of the books is horizontal

C) A chair is lifted vertically with respect to the floor. --> work is done, because the force that lifts the chair is vertical, and the displacement is vertical as well

D) A table is dropped onto the ground. --> work is done, because the force of gravity (that makes the table falling down) is vertical and the displacement of the table is also vertical.